The ETS2 promoter contains an extended region of purine/pyrimidine strand asymmetry (CT track) upstream from the start site for transcription. The presence of these sequences are required for full ETS2 expression. At least two regions of the CT track that form protein complexes in the electrophoretic mobility shift assay (EMSA) have been identified. The major complex was found to compete well with a transcription factor Sp1 consensus oligonucleotide. It was also found to comigrate with the protein complex of pure Sp1 and to supershift with antibodies raised against Sp1. Both Sp1 and nuclear extracts exhibit similar DNaseI footprint patterns. A protein-DNA complex in the EMSA that forms with single-strand DNA was observed. It has a binding sequence specificity that is very similar to the Pur-alpha factor. However, the mobility of complexes that form with the factor from nuclear extracts differs from that of recombinant Pur-alpha.